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法学如何在 MongoDB 中获取特定字段作为结果？
要获取 MongoDB 中的某个字段作为结果，你可以使用 findOne()。以下为语法：-
db.yourCollectionName.findOne({"yourFieldName1":yourValue},{yourFieldName2:1});让我们先用文档创建一个集合：-
> db.particularFieldDemo.insertOne({"EmployeeName":"John Smith","EmployeeAge":26,"EmployeeTechnology":"MongoDB"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9b4abb50a6c6dd317ada2")
}
> db.particularFieldDemo.insertOne({"EmployeeName":"Chris Brown","EmployeeAge":28,"EmployeeTechnology":"Java"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9b4d2b50a6c6dd317ada3")
}
> db.particularFieldDemo.insertOne({"EmployeeName":"David Miller","EmployeeAge":30,"EmployeeTechnology":"MySQL"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9b4e8b50a6c6dd317ada4")
}
> db.particularFieldDemo.insertOne({"EmployeeName":"John Doe","EmployeeAge":31,"EmployeeTechnology":"C++"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9b527b50a6c6dd317ada5")
}以下为使用 find() 方法在集合中显示所有文档的查询：-
> db.particularFieldDemo.find().pretty();
这将生成如下的输出：-
{
"_id" : ObjectId("5cd9b4abb50a6c6dd317ada2"),
"EmployeeName" : "John Smith",
"EmployeeAge" : 26,
"EmployeeTechnology" : "MongoDB"
}
{
"_id" : ObjectId("5cd9b4d2b50a6c6dd317ada3"),
"EmployeeName" : "Chris Brown",
"EmployeeAge" : 28,
"EmployeeTechnology" : "Java"
}
{
"_id" : ObjectId("5cd9b4e8b50a6c6dd317ada4"),
"EmployeeName" : "David Miller",
"EmployeeAge" : 30,
"EmployeeTechnology" : "MySQL"
}
{
"_id" : ObjectId("5cd9b527b50a6c6dd317ada5"),
"EmployeeName" : "John Doe",
"EmployeeAge" : 31,
"EmployeeTechnology" : "C++"
}以下为在 MongoDB 中查找某个字段作为结果的查询：-
> db.particularFieldDemo.findOne({"EmployeeTechnology":"Java"},{EmployeeName:1});这将生成如下的输出：-
{
"_id" : ObjectId("5cd9b4d2b50a6c6dd317ada3"),
"EmployeeName" : "Chris Brown"
}
更新于： 2019 年 7 月 30 日
98 次浏览
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